I am using JSch and connection and session objects not inherited in subclass

Question

import com.jcraft.jsch.ChannelExec;
import com.jcraft.jsch.JSchException;

public class ImageTypeDeployer extends MainImageDeployer {

public ImageTypeDeployer(String VolID,String oS,String imageName){

    String command="some command"

    try {        
        channel=session.openChannel("exec");
        channel.setInputStream(null);
        ((ChannelExec)channel).setCommand(command);
        channel.connect();
    } catch (JSchException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}   

}

I am getting a NullPointerException on the line channel = session.openChannel("exec") and the same thing works when I put the code in the superclass. Is this because session and channel variables are not inherited or is it something else ?

This is the superclass code where I am making a connection.

public void makeAConnection(){

    inputFile = RESTEngine.getFilePath();
    Properties defaultProps = new Properties();
    try {
        fin = new FileInputStream(inputFile);
        defaultProps.load(fin);
        fin.close();
    }
    catch(FileNotFoundException e1){
        System.out.println("The properties file supposed to contain PowerVC Authorization parameters was not found.");
        e1.printStackTrace();
        System.exit(-1); 
    }
    catch(IOException e1){
        System.out.println("An exception occured while trying to open the properties file");
        e1.printStackTrace();
        System.exit(-1);
    }
    // assign variables from Input file with default value as null
    user = defaultProps.getProperty("UserID", null);
    host = defaultProps.getProperty("PowerVC_IP_ADDRESS", null);
    password = defaultProps.getProperty("UserPass" ,null );

    jsch = new JSch();
    try {
        session = jsch.getSession(user, host, 22);
        session.setPassword(password);
        java.util.Properties config = new java.util.Properties(); 
        config.put("StrictHostKeyChecking", "no");
        session.setConfig(config);
        session.connect();
        channel=session.openChannel("exec");
        channel.setInputStream(null);

        try {
            in = channel.getInputStream();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        System.out.println("Connection Successful");
    } catch (JSchException e) {
        // TODO Auto-generated catch block
        System.out.println("Unable to connect");
        e.printStackTrace();
    }

}

This is how I am calling the ImageTypeDeployer

protected Boolean doInBackground() throws Exception {

    makeAConnection();
    for(String imageName : volIDMap.keySet()){

        String volID = volIDMap.get(imageName);
        String oS = osMap.get(imageName);
        if (oS.equalsIgnoreCase("aix")){

            MainImageDeployer imageDeployer = new ImageTypeDeployer(volID, oS, imageName);

        }


    }
    return null;



}

Answer 1

It appears the session field is not initialized in the constructor of ImageTypeDeployer or any of its superclasses, so it is null when you try to call session.openChannel. That explains the need to initialize it in your makeAConnection method.